The present invention relates to the use of light-emitting, solid-state compositions as a light source for laser pumping and laser systems containing same.
In conventional laser systems, active atoms or molecules of a lasing medium (gas, liquid, or solid type) are "pumped" by a source of exciting energy. This optical pumping excites the active atoms or molecules into a higher or excited energy level. When the number of atoms/molecules in the excited state reaches a certain threshold level (i.e., the level at which the number of excited active atoms in the upper laser state is greater than the number of active atoms in the lower laser state), light of sufficient energy can then induce or stimulate the excited atoms/molecules to make the transition to the ground state, causing light emission and amplification. In addition, lasers are generally provided with resonators which cause the emitted light to further amplify and increase in intensity. In certain situations, for example, if the gain is high enough, resonators may not be necessary.
In optically pumped lasers, which may be liquid, gas, or solid lasers, the source of exciting energy or pumping means is often a source of electromagnetic radiation.
Examples of such pumping means are flash lamps such as xenon-filled glass or quartz tubes. These lamps are made to flash by discharging a high voltage through the xenon gas. Other pumping means are mercury arc lamps, light-emitting semiconductor diodes, and other lasers.
Flash lamps emit light over a broad wavelength band. Their pumping efficiency is, therefore, low because the absorption band of the lasing material almost always comprises only a small portion of the flash lamp emission spectrum. For example, conventional flash lamps generally emit a continuous spectrum of light, from ultraviolet, through visible, and into the infrared range. Conversely, titanium sapphire, a lasing material, has a peak adsorption at about 470 nm. Thus, most of the light emitted by a conventional flash lamp is wasted.
In many cases, lasers cannot be made from potentially useful materials because the intensity required exceeds what a flash lamp could provide due to the optical opacity of the discharge or the ultimate power delivery limits of the flash lamps themselves. In other words, for some potential lasing materials, the maximum light intensity of flash lamps may not be adequate to achieve the threshold for lasing. Generally, the maximum power of conventional flash lamps is several megawatts per cubic centimeter at peak intensity.
The duration of the pumping pulse can be a determining factor of a laser's power. The pumping pulse is the actual period of the optical energy emission from the pump source. For many high power lasers, the pumping pulse duration must be shorter than the fluorescence lifetime of the excited state. The more energy that can be pumped into the laser during that time, the more active atoms/molecules will be excited and the more probable the lasing material will reach the threshold level necessary for stimulated emission.
If the pump pulse duration exceeds the fluorescent lifetime, the laser may still lase if the pump rate, the rate at which active atoms/molecules are excited into the upper energy level, exceeds the deactivation rate, the rate at which excited atoms/molecules decay to the ground state. Generally, though, it is desirable to have a pumping pulse which is shorter than the fluorescent lifetime.
The pumping pulse duration of flash lamps is generally slow, typically on the order of milliseconds. For many popular applications, the pulse duration is about 0.1-10 milliseconds. High power lasers pumped with such flash lamps, therefore, must have relatively long fluorescent lifetimes, e.g., on the order of milliseconds. Flash lamps can sometimes operate in a continuous mode, but this is highly dependent on the characteristics desired by the laser designer.